Inertia sensors are used in seat belt retractors, for example, to control a blocking device upon the exceeding of a predetermined vehicle deceleration. The inertia sensor itself has for that purpose an inertia mass placed in a sensor housing which is deflected in the sensor housing upon a predetermined vehicle deceleration which is determined by the suspension of the inertia mass and the mass of the inertia mass. Upon deflection, the inertial mass raises a blocking lever, which in order to control the blocking device guides into an externally geared control disc rotatably mounted on the belt shaft of the seat belt retractor and stops the control disc with respect to the belt shaft. The predetermined vehicle deceleration, or also a threshold of the inertial sensor at which the seat belt retractor must block, is an essential, safety-related, functional criterion of the seat belt retractor and is therefore legally prescribed. In order for the seat belt retractor to meet the legal requirements, the response threshold may not in any case be so changed, that the seat belt retractor is first blocked in the direction of belt extraction above the predetermined vehicle deceleration.
Basically seat belt retractors with inertia sensors having a swiveling sensor housing are always used when the seat belt retractors are to be placed in a vehicle structure that can have an adjustable incline or in general perform their function in various angular orientations. For example, a seat belt retractor may be mounted to an occupant's seat which has an adjustable reclining or adjusted position. For such applications, the inertial sensor needs to respond to the vehicle decelerations in a similar manner over a range of adjustment positions of the retractor. Accordingly, a swiveling sensor housing may be used which becomes adjusted in response to a change in the position of the retractor frame. Because of the swiveling sensor housings the inertia sensor can swivel into various angular positions with respect to the seat belt retractor, such that it can exhibit a defined angular orientation to the vehicle or to the direction of gravity independent of the incline of the seat belt retractor.
One problem of such inertia sensors with swiveling sensor housings is that the sensor housing itself can swivel with respect to the seat belt retractor, e.g. during a strong braking of the vehicle, whereupon in this case the response threshold of the inertia sensor can change, since the inertia mass also executes the swivel movement of the sensor housing and thus only deflects in a delayed manner.
In order that the response threshold is not unintentionally changed because of the above-stated problem, it is known from DE 10 2005 029 487 B4 how to fix the sensor housing during the belt extraction movement by means of a blocking element. The blocking element is positioned on the frame of the seat belt retractor so as to swivel and engages into an outer gearing of the sensor housing in a position blocking the sensor housing. The movement of the blocking lever is controlled in this solution by a control lever, frictionally connected on the belt shaft, which engages into a control contour of the blocking lever and guides the blocking lever out of the gearing of the sensor housing during the belt retraction movement. Furthermore, the blocking element is spring-loaded in the direction of the engaged position into the gearing of the sensor housing by means of a spring supported on the frame of the seat belt retractor, so that after the end of the belt retraction movement, the blocking element again travels independently into the gearing of the sensor housing and fixes the sensor housing. As a result, the return movement of the blocking element is facilitated in particular in this case, since the control lever is connected to the belt shaft by means of a friction coupling which exhibits higher dynamic friction coefficients in relation to the static friction coefficients.
Needed overall to design this system is a fine tuning of the spring loading of the blocking element and the connection of the control lever to the belt shaft and also a very good guiding of the control lever into the control contour of the blocking element.